once again..."vocaloids" are not characters, they are instruments. they are not fictional persons that belong to an authored narrative, they are real-world tools for producing art. official info is not a "canon," it is a suggestion of a starting point for further interpretation.
a suggested starting point for piano music might be classical music, but feel free as a musician to use a piano in WHATEVER genre of music about WHATEVER topic of music you want. piano is an instrument. VOICE is ALSO an instrument. it CAN and IS used across the musical arts.
the VOICE is the strongest musical instrument a /PERSON HAS/. why WOULDN'T a vocal instrument have an attached character design?? it also helps differentiation and gives people a little more to work with and interpret/derive than a disembodied voice????
vocaloid is fundamentally unlike the vast majority of works central to fandoms, not because I Like It And Therefore It's Special, but because it's not a show, movie, novel, comic, game...it's not a FINISHED, AUTHORED, PUBLISHED WORK. it's a malleable, shared, active tool.
there aren't usually FANDOMS for tools. sure PLENTY of people use, idk, pens? paint? sewing machines? makeup? violins? Clip Studio Paint? Zbrush? but you're gonna need a little more than that to unite people and establish a cultural phenomenon.
vocaloid understands that recognizable source material is needed to unite fandom, but doesnt treat said source material as "the one true canon," it harnesses the fact that it's a TOOL to say "with this instrument, YOU create the canon" and equalizes everyones art in authenticity.
yknow what's another thing half-tool half-fandom? Minecraft. recognizable source material-- but no canon, for the express purpose of empowering people to build whatever they want, create whatever characters they want, tell whatever stories they want. it's like that.
there are no characters in vocaloid, besides interpretations created BY producers, animators, illustrators, etc-- meaning there are thousands and thousands of Mikus. and vocaloids that arent even Miku. hell, /OCs/ that just HAPPEN to be in vocaloid music.
but if you're NOT talking about any of those specific authored "Mikus" (e.g. Nashimoto-ui's depressed 'husky' Miku, Mitchie-M's cheery 'realistic' Miku, etc), and just...CFM Miku, official Miku, V2-boxart-Miku? you're talking about an instrument. not a character.
default Miku's design (and the CFMloids in general, who by and large established the decentralized indie-focused culture vocaloid has today) is basically a 'gijinka' personification of the vocaloid voice synthesis software interface itself. that's why it looks scifi-like.
do whatever you want with vocaloid. it's pen and paper in the form of a voice that anybody can use. just don't do anything with vocaloid you wouldn't do with pen and paper? like idk if you wouldnt draw p*do shit, then dont sing about it either, its really that simple.
anyway i know vocaloid/miku on the surface in a lot of ways looks like any other anime-styled virtual-idol thing out there. but yknow? it's not. we have "characters" because in the end it's fun. to imagine what's technically a disembodied voice as WHOever you want it to be.
music, unlike novels/shows/games, don't tend to have super complex fictional fantasy lore. by and large the majority of topics touched on by music (vocaloid music included of course) are simply real people's real experiences, thoughts, and feelings that they wanted to express.
vocaloid, instead of being a produced finished work released for audience consumption with the message to "express yourself," IS FUNDAMENTALLY a collaborative ever-changing instrument released for audience creation with the means to express yourself.
my stance on creating artworks featuring mature themes with vocaloid is simply that if you wouldn't make it with pen+paper, paint, clay, spoken word, written word, animation, dance, film, photography, game design, ANY instrument designed for creative expression-- then don't.
again, "vocaloids" are instruments, and "characters" are personal interpretations of said instruments. someone using an underaged interpretation for sexually mature artwork isn't a problem because "Miku is 16," it's a problem because they're CHOOSING to use an underage person.
i alongside MANY voca fans object to the "Miku is 16" argument not because we think it's okay to use 16yo's for sexual content, but because what should/shouldn't be done with voca should be judged alongside other instruments that function in similar ways for similar purposes,
not the plethora of unrelated published authored works that voca as a tool shares very little in common with. "aging up" characters for sexual artwork is a problem for most franchises because characters have canon, fixed representations.
with voca, that's simply not the case. "authoritative authenticity" is not held by the parent company(s) that produce fixed representations, it is held by US as artists that produce varying interpretations. YOU write the canon.
YOU are enabled to make whatever you want. YOU are responsible for not casting underage persons, fictional or not, in sexual work. there's no reason not to, especially when voca is inherently designed in such a way that you are MEANT to change+alter the official starting-points.
the furthest i think i'll put my foot down is that people shouldn't use like..Kaai Yuki for sexual content, not because "the character is a child," but because the VOICE PROVIDER herself is (was) a child and thus the voice itself, regardless of how you use it, belongs to a child.